Question

if 26 term of an ap is 10 find the sum of the first 51 term of ap

Answer 1

an=a+[n-1]d

a26=a+[26-1]d

10=a+25d

Sn=n/2[2a+{n-1}d]

s51=n/2[2a+{51-1}d]

s51=n/2[2a+50d]

• taking 2 as common , we get

=n/2×2[a+25d]

n=51

51×10

• we get the answer as

=510